Numerous studies have suggested that modifiable factors like diet and exercise are associated with risk for Alzheimer’s, but a comprehensive review of the data suggests there is not enough evidence to firmly link the two -- for now.

“Alzheimer’s is the only disease in the top 10 causes of death [in the U.S.] that doesn’t have a way to slow it down, or prevent it,” said Dr. Maria Carrillo, senior director of medical and scientific relations at the Alzheimer’s Association.

The report, published online today in the journal Archives of Neurology, reiterates the findings of a panel convened by the National Institutes of Health last spring. Tasked with reviewing pertinent research from the past several decades, the panel found no conclusive evidence linking lifestyle choices with risk for the disease. At present, the strongest known risk factors for Alzheimer’s are age, as well as a variation in the APOE gene.

“We are not saying that these modifiable factors are not going to be associated [with Alzheimer’s],” said Dr. Martha Daviglus of Northwestern University’s Feinberg School of Medicine and the report’s lead author. “We are just saying that there is not enough high-quality data now.”

The panelists did find that many studies showed an association between Alzheimer’s and modifiable factors like diet and exercise, alcohol intake, hypertension, diabetes, high cholesterol and smoking. They also reviewed multiple studies linking cognitive engagement with development of Alzheimer’s.

But while many showed promise, the researchers concluded that overall the studies suffered from methodological issues, including inconsistent use of diagnostic criteria as well as a reliance on self-reported information. They called for large-scale, long-term studies and clinical trials designed specifically to better address the issue.

The good news, Daviglus said, is that several such efforts are currently underway:

Depending on how homogeneous the outcomes are, it could be just a few years until we know with certainty about some modifiable risk factors.

But she added that further longitudinal studies, which could take decades, are also necessary. Such research is expensive, which is why organizations like the Alzheimer’s Association are focused on funding them a public and federal priority.

“What we really need is a public and private partnership, with a long Framingham-type study that looks at brain health over time,” Carrillo said. The Framingham Heart Study began in 1948 with the aim of better understanding the development of cardiovascular disease; it has now tracked three generations of participants.

Those interested in preventing Alzheimer’s should not despair; researchers say they should maintain or adopt new healthy modifiable behaviors, regardless of where the science stands. Carrillo said people should pay particular attention to physical activity, because it has been suggested it can not only biologically reduce the effects of Alzheimer’s, but also cognitive changes over time. She added that people can consult the Alzheimer's Association website for a full list of recommendations.

Daviglus agreed.

“What I would say to people is that they should continue to have good eating, they should continue exercising and they should continue doing all of these good things," she said. “We know that these modifiable risk factors will help with many chronic diseases, and maybe even with Alzheimer’s.”